The present invention relates to novel chiral 1,1xe2x80x2-ferrocenylene diphosphonites and the synthesis thereof, in addition to complexes of said compounds with metals from groups VIIb, VIIIb and Ib of the Periodic Table and to the use thereof for enantioselective hydrogenation of olefins, ketones and imines.
In the last 20 years, the catalytic enantioselective synthesis has gained importance in industry, e.g., the transition-metal catalyzed asymmetric hydrogenation (B. Cornils, W. A. Herrmann, Applied Homogeneous Catalysis with Organometallic Compounds, Wiley-VCH, Weinheim, 1996; R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994). Rhodium, ruthenium or iridium complexes of optically active diphosphanes such as BINAP (R. Noyori et al., J. Am. Chem. Soc. 1980, 102, 7932), DuPHOS (M. J. Burk et al., J. Am. Chem. Soc. 1995, 117, 9375), BICP (X. Zhang et al., J. Am. Chem. Soc. 1997, 119, 1799) and BPE (M. J. Burk et al., J. Am. Chem. Soc., 1996, 118, 5142) are usually used as catalysts. Drawbacks in these systems include the relatively high preparative expenditure in the preparation and, if necessary, optical resolution of the racemic ligands and the frequently insufficient enantioselectivity observed in catalysis. Therefore, it has been the object of industrial and academic research to prepare novel and particularly well-performing ligands in as simple a way as possible.
In contrast to diphosphanes, chiral diphosphonites as ligands in catalysis have been described only in two cases (L. Dahlenburg et al., J. Organomet. Chem. 1998, 564, 227, and Eur. 3. Inorg. Chem. 1998, 1, 885, and I.E. Nifant""ev et al., Russ. J. Gen. Chem. 1995, 65, 682.).
In the first case, diphosphonites were used which are derived from optically pure 1,2-bis(dichlorophosphino)cyclopentane and achiral monovalent alcohols or optically pure (R)-binaphthol. In the rhodium-catalyzed hydrogenation of 2-acetamidocinnamic acid, a maximum enantiomeric excess of 78% could be achieved using such ligands in the case of the corresponding phenol-derived diphosphonite. The substrate-to-catalyst ratios used were extremely low in all cases (76:1). In addition, it is pointed out that there are significant preparative difficulties in the preparation of the rhodium complexes of these ligands. These are two serious drawbacks preventing practicability.
Nifant""ev et al. used ferrocenylene diphosphonites based on protected monosaccharides, namely C1-symmetric aliphatic 1,2-diols (2 examples) and 1,3-diols and C2-symmetric aliphatic 1,4-diols (1 example each). Rhodium complexes of these ligands were synthesized from [Rh(CO)2Cl]2 as a precursor and employed in the asymmetric hydrosilylation of acetophenone. The highest value of enantiomeric excess achieved was 32%, chemoselectivity also being insufficient, so that commercial usefulness can be excluded.
However, according to our results, ferrocenylene diphosphonites are ligands having excellent properties when suitable chiral diols are selected as the starting materials. In addition, they can be prepared very easily and inexpensively. It was found that useful diols primarily include C2-symmetric aliphatic 1,2-diols or axially chiral aromatic or heteroaromatic diols. Thus, not only the selection of a suitable backbone, ferrocene in the present case, but also the selection of suitable diols is essential for a successful application of diphosphonites. The two examples known to date from the literature (see above) left this point unconsidered, so that practicable results could not be achieved to date. The present invention includes the first example of chiral diphosphonites in general with which enantioselectivities of more than 99% in asymmetric catalysis and thus selectivities useful for practical applications can be achieved.
The basic idea of the present invention includes chiral C2-symmetric diphosphonites with ferrocene as the backbone containing either chiral C2-symmetric 1,2-diols with an aliphatic base structure or axially chiral aromatic or heteroaromatic diols in the P/O heterocycle, and their synthesis. The invention also includes metal complexes of such ligands and their use in asymmetric synthesis. Ligands of this type exhibit excellent enantioselectivities in the hydrogenation of various prochiral olefins, but can be prepared clearly more simply and therefore less expensively as compared to systems known to date from the literature having a comparably high selectivity (e.g., DuPHOS or PennPHOS; M. J. Burk et al., J. Am. Chem. Soc. 1995, 117, 9375, and X. Zhang et al., Angew. Chem. 1998, 110, 1203).
In detail, the invention comprises 1,1xe2x80x2-ferrocenylene diphosphonites of types I, II, III and IV. 
In the case of class I of compounds, the building blocks are C2-symmetric chiral diols of type V. 
Residue R1 can be a saturated hydrocarbon which may optionally be functionalized, such as in the case of 1,2-diol units of protected carbohydrates or protected aminoalcohols. Possible residues also include aromatic or heteroaromatic groups, such as phenyl, naphthyl or pyridyl, which can themselves be functionalized as desired. Finally, it is possible for the residues to consist of ester or amide groups, such as xe2x80x94CO2CH3, xe2x80x94CO2C2H5, xe2x80x94CO2xe2x80x94ixe2x80x94C3H7 or xe2x80x94CO[N(CH3)2], xe2x80x94CO[N(C2H5)2] or xe2x80x94CO[N(ixe2x80x94C3H7)2], the corresponding diols V being tartaric acid derivatives.
In the case of class II of ligands, the oxygen-containing building block consists of binaphthol VI with residues R1, R2, R3, R4, R5 and R6, which may independently represent the following groups: hydrogen (H), saturated hydrocarbons, optionally functionalized and/or bridging (e.g., R1+R2=xe2x80x94(CH2)4xe2x80x94), aromatic or heteroaromatic groups which may also be functionalized and/or condensed and thus represent cyclic residues (for example, R1+R2=ortho-phenylene; corresponding to 4,4xe2x80x2-dihydroxy-5,5xe2x80x2-bis(phenanthryl)), non-aromatic unsaturated hydrocarbons, such as alkynyl groups xe2x80x94Cxe2x89xa1CR, which may also be functionalized, silyl groups, such as xe2x80x94SiMe3, halogens (xe2x80x94Cl, xe2x80x94Br, xe2x80x94F, xe2x80x94I), nitro (xe2x80x94NO2) or nitrile (xe2x80x94CN) groups, or esters (xe2x80x94CO2R), amides (xe2x80x94C(O)NRRxe2x80x2), amines (xe2x80x94NRRxe2x80x2), ethers (xe2x80x94OR), sulfides (xe2x80x94SR) and selenides (xe2x80x94SeR), wherein R and Rxe2x80x2 are hydrogen, saturated or non-aromatic unsaturated hydrocarbons which may optionally be functionalized, or aromatic residues which may optionally be functionalized. In particular, the present invention includes all combinations of the residues mentioned for R1, R2, R3, R4, R5 and R6 including all C1- and C2-symmetric substitution patterns of the binaphthol base structure. Further, one or more carbon atoms of the binaphthol core may also be replaced by heteroatoms, such as nitrogen. Preferably, binaphthol (R1=R2=R3=R4=R5=R6=H) itself serves as a building block. 
In the case of class III of compounds, the dihydroxy building block is a functionalized, configuratively stable biphenol VII. Configurative stability with respect to axial chirality is ensured when R4xe2x89xa0H (E. L. Eliel, S. H. Wilen, L. N. Mander, Stereo-chemistry of Organic Compounds, Wiley, New York, 1994). R1 to R4 have the same range of variation as residues R1 to R6 in the case of class VI of compounds. Preferably, however, R1=R2=H, and R3+R4=xe2x80x94(CH2)4xe2x80x94 (2,2xe2x80x2-dihydroxy-5,5xe2x80x2,6,6xe2x80x2,7,7xe2x80x2,8,8xe2x80x2-octahydro-1,1xe2x80x2-binaphthyl, D. J. Cram et al., J. Org. Chem. 1978, 43, 1930). 
In the case of class IV of compounds, the dihydroxy building block is a functionalized, configuratively stable heteroaromatic system VIII derived from 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-bis(indolyl) (X=N), 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-bis(benzo[b]thiophenyl) (X=S) or 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-bis(benzo[b]furanyl) (X=O). In these cases too, the substituents have the same range of variation as in VI. Substituent R1 is absent in the cases where X=O or X=S. 
The present invention encompasses all stereo-isometric forms of diols V, VI, VII and VIII as building blocks.
Scheme 1 illustrates the synthetic path for the ligands according to the invention. In thie first step, a twofold lithiation of ferrocene with n.-butyllithium in the presence of tetramethylethylenediamine (TMEDA) as known from the literature (J. J. Bishop et al., J., Organomet. Chem. 1971, 27, 241) is effected, followed by phosphorylation with phosphorus chlorides, such as CIP[N(CH3)2]2 or CIP[N(C2H5)2]2, to form class IX of compounds; in the second step, these are reacted with diols V, VI, VII or VIII to form the ligands I, II, III or IV, respectively. 
Scheme 1
A variant of this synthesis includes an additional step, i.e., the reaction of IX with HCl to form X, which is then reacted with diols V, VI, VII or VIII (Scheme 2). In many cases, this increases the overall yield. 
Scheme 2
The invention also includes the formation of novel metal complexes by reacting the ligands according to the invention with transition metal compounds usually employed with diphosphines, especially metals of Periodic Table groups VIIb, VIIIb and Ib (see, e.g., B. Cornils, W. A. Herrmann, Applied Homogeneous Catalysis with Organometallic Compounds, Wiley-VCH, Weinheim, 1996; R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994). Examples include Rh, Ru, Ir, Ni, Pd or Cu complexes of types XI-XXXVIII (wherein cod stands for xcex72:xcex72-1,5-cyclooctadiene, and cymol stands for xcex76-1-iso-propyl-4-methylbenzene). 
Finally, the invention also includes the use of the metal complexes according to the invention as catalysts in asymmetric catalysis, such as hydrogenation, hydroformylation, hydrocyanation, hydrosilylation, hydrovinylation, hydroboration and copper-catalyzed 1,4-addition. Examples include the asymmetric hydrogenations of dimethyl itaconate XXXIX, 2-acetamidomethyl acrylate XL, (Z)-2-acetamidocinnamic acid XLI and its methyl ester XLII, xcex1-acetamidostyrene XLIII and N-(1-phenylethylidene)aniline XLIV, which can be performed with very high chemical yields and enantioselectivities when the metal complexes according to the invention are used. The same applied to the hydroboration of styrene VL, and the copper-catalyzed 1,4-addition to 2-cyclohexene-1-one VLI or 2-cycloheptene-1-one VLII.
These results are of high practical relevance, which makes these compounds interesting for industrial applications as well. 